Semiconductor nanostructures can be incorporated into a variety of electronic and optical devices such as photovoltaic devices and LEDs. The electrical and optical properties of these nanostructures vary depending on their composition, shape, and size. Group III-V semiconductors exhibit a number of desirable electrical properties such as low energy and direct band gap behaviors and high electron mobility, as well as other desirable properties such as thermal stability.
Methods for simply and reproducibly producing Group III-V semiconductor nanostructures—nanostructures of different sizes, shapes, and combinations thereof—are desirable. In some embodiments, the present invention provides such methods.
A traditional method for the synthesis of InP nanocrystals uses the commercially available precursor material In(OAc)3 (Ac=OCCH3). In a typical reaction, commercially available In(OAc)3 is treated with a long-chain carboxylic acid in a reaction that removes acetic acid and forms a new material that is suitable for conversion to InP nanocrystals. Because In(OAc)3 is both hydroscopic and moisture sensitive, it must be handled using inert atmosphere conditions requirements that increase production costs and require extensive purification of the other reagents used to remove any trace amounts of water.
Furthermore, upon exposure to moisture or humidity, In(OAc)3 undergoes partial hydrolysis to form a mixture corresponding to the formula In(OAc)3-n(OH)n, wherein 0≤n≤1. It has been found that many commercially available samples sold as “indium acetate” are actually mixtures having the formula In(OAc)3-n(OH)n.
Use of In(OAc)3-n(OH)n in the typical synthesis of InP nanocrystals has several drawbacks. Firstly, since the reagent used is a mixture, the synthetic method will not produce consistent nanocrystal products. This is because a mixture will not allow one in the art to know and control the ratio of In3+ to long-chain carboxylic acid. Secondly, treatment of In(OAc)3-n(OH)n with long-chain carboxylic acids is expected to form In(O2C(CH2)mCH3)3-n(OH)n upon ligand exchange. It is likely that In(O2C(CH2)mCH3)3-n(OH)n is not suitable for nanocrystal growth due to the high sensitivity of the reaction kinetics. Thus, if In(O2C(CH2)mCH3)2(OH) and In(O2C(CH2)mCH3)3 react at different rates, the precursor conversion in nanocrystal growth—a step that is critical for obtaining a narrow size distribution—will be more difficult to control than when a single reaction material is used. Therefore, if the value of n is not controlled, then the nanocrystal growth reaction may be irreproducible between batches.
Therefore, a need exists to identify a precursor material that not only can be handled in open air conditions without special treatment but also is stable for long periods of time and thus, allows the amount of indium used as a reagent to be precisely controlled.